With fuel cells being desired for automotive propulsion purposes, it has become important for fuel cells to achieve full power quickly. This requires a rapid increase from ambient temperature to normal operating temperature.
Electrochemical fuel cells convert fuel and oxidant into electricity, a reaction product (such as water in the case of a hydrogen fueled and oxygen oxidizing fuel cell), and heat. The fuel cell typically has a membrane electrode assembly (“MEA”) separating the fuel from the oxidant. The MEA is where the reactions take place and contains the catalyst needed to accelerate the reaction.
The MEA can be damaged by the simultaneous presence of air and hydrogen in the anode. The amount of damage is determined by the cell voltage with higher voltages leading to greater damage. The time when this is most likely to occur is during fuel cell startup.
Because fuel cells typically produce low voltages, they are often organized into a stack of multiple cells connected in series. This allows them to combine to produce higher voltages.
One way to accelerate reaching an appropriate power level is to have the fuel cell stack short together its fuel cells. This holds down the voltage causing the fuel cells to produce extra heat that is supplemented by the resistive heating provided by the shorting element. The extra heat from both sources can speed the cell toward reaching normal operating temperatures where higher efficiencies can be achieved.